May 2013

Symmetry and within-session reliability of mechanical properties of biceps brachii muscles in healthy young adult males using the MyotonPRO device

K. Mooney, M. Warner, M. Stokes
Faculty of Health Sciences, University of Southampton
Working Papers in Health Sciences (Spring 2013, ISSN 2051-6266 / 20130011)

Objective measurement of muscle tone and mechanical properties is generally challenging in clinical or sports
settings and can be obtained using a novel hand-held device (MyotonPRO). Between-side comparison of muscle function and characteristics can assess abnormalities if normal symmetry is known, which this study investigated for biceps brachii (BB).

To examine between-side symmetry of mechanical muscle parameters and within-session intra-rater reliability of
testing the BB muscle.

Methodological, observational, intra-rater reliability study.

Convenience sample (n=21 ) of healthy males, aged 18-35 years.

The participant lay supine with the elbow in slight flexion (10-15 degrees). The MyotonPRO applied brief, low force
mechanical impulses over BB muscle belly eliciting damped oscillations, from which non-neural tone (frequency; Hz), dynamic stiffness [N/m] and elasticity (logarithmic decrement) were calculated automatically. Two sets of 10 impulses were applied bilaterally by a novice user. Actual, absolute and percentage differences between sides were calculated to assess symmetry. Within-session reliability was assessed using intra-class correlation coefficients (ICC), standard error of measurement (SEM), and Bland and Altman analysis.

Mean and standard deviation (±) absolute and percentage differences were 14±11N/m (6 ± 5%) for stiffness 0.6 ±
0.4Hz (4 ± 3%) for tone, and 0.08 ± 0.08 logarithmic decrement (7.5 ± 7%) for elasticity. Within-session reliability was excellent for all three parameters (ICC3,2>0.95). The SEMs were 2.3N/m (stiffness), 0.1Hz (tone); and 0.03 for decrement (elasticity). Bland and Altman analysis showed minimal systematic bias between sets ( d =-1.9N/m, -0.1Hz; and 0.05 decrement).

Symmetry of mechanical parameters for the BB muscle in healthy young males were 4% for tone, 6% for stiffness and 8% for elasticity. Unlike muscle strength, the side of the greater value was not determined by limb dominance and the method of comparing values between sides influenced the level of symmetry found, so calculation of absolute rather than actual differences is recommended to reflect true symmetry.

The findings indicate the potential for using asymmetry of Myoton parameters of >10% as a measure of abnormality for BB in young males but this threshold needs to be confirmed in larger numbers of participants and cannot be generalised to other muscles or participant groups. A novice user achieved excellent intra-rater reliability within the same session for all three parameters tested.Further research is warranted to determine the ability of the MyotonPRO to establish normal symmetry and variability within age, gender and sport-specific participant groups.